The problem is, I think I myself might not have even commented in the thread, so it is hard to search for... anyway, I think it is unlikely to be you, because I wouldn't have laughed at a demand for evidence if it was about legislating a helmet mandate (sure better have real evidence in that case!) but it was more like "I crashed and hit my head on the curb, thank god I was wearing a helmet!").
(I myself mainly get around Tokyo on my VanMoof X2 ebike and almost never wear a helmet...)
You've motivated me to keep searching for the comment now, though... ;-)
(The comment I am looking for also started rather emotionally, something like "Ugh I hate — HATE — when people... (make assumptions like this without evidence, something something)". And then possibly invoked the names of a couple of logical fallacies.
(T_T) I thought I'd be able to find it with the double "hate", but I can't... it was some years ago too, at least 4-5, so I am probably mis-remembering.
> I am always annoyed with articles promoting safe cycling when illustrating pictures show cyclists without helmets or any other form of protective gears.
> In Belgium there is a small movement promoting bikes and there are all kind of hipsters, bobo and 50 years old grey hair vegan on fake vintage bikes riding without helmets and without any sense of road conduct. Good bikers wearing yellow jackets and helmets are really rare ; I am beginning to think the formers are ruining the latters's image.
Strangely neither can I find those comments at the time.
I have the fuzzy memory that it was about a bikes around Sydney or Australia but HN comments tend to derail from the initial submission so I can't be sure.
edit: found it ! https://news.ycombinator.com/item?id=4262081